Vacuum tube and method of making same



Aug. 25, 1936. A. J. MCMASTER VACUUM TUBE AND METHOD OF MAKING SAME Filed May 14, 1932 w J f -"latented `Aug. 25,`

I UNrrlazDI STATE-s VACUUM TUBE AND METHOD 0F MAKING SAME Archie J. McMaster, Highland Park, Ill., assigner to G-M Laboratories, Inc., Chicago, Ill., a corporation of Illinois Application May 14, 1932, Serial No. 611,255

4 Claims. (Cl. 49-78) My invention relates in general to bulb construction and method for making the same, and more particularly to the method of attaching an exhaust tube to such bulbs. l

In the manufacture of electric lamp bulbs,

radio tubes, and the likefr'om which it is necessary to exhaust the air, various methodshave been used to attach an exhaust tube for con- "necting the bulb to a vacuum pump. For many years it has been desirable Ito connect the exhaust tube to a part of the bulb vsuch that the exhaust tube tip when it is sealed ofi` from the pump, can be readily covered by a base or fitting through which connecting Wires are also brought out. Such constructionk reduces the fragilitygof the bulb because the tip of the exhaust tube is not exposed to the hazard of breakage after the base is attached.

An object of this invention is to provide a bulb having an exhaust tube sealed to the stem of the bulb.

A further object is to provide a type of bulb construction which will be economical to manufacture. L

A further object is to provvide a method of manufacturing such bulbs in which thev production shrinkage due to imperfect results will be reduced toa minimum.

Atfurther object is to provide a bulb construcl' ,30 tionwhichwill lbe stronger and'less fragile during `subsequent''operationsgin the manufacture of the completed 'article beforethebase is attached.

y Other objects and'advantages will appear las l thel description proceeds.

AFor a better understanding of this invention reference is made to the accompanying drawing, wherein,

Fig. 1 shows a completed bulb made in accordance with my invention.

Fig. 2 is a view of the component parts of the stem of such a bulb mounted on a wire die block of a stem making machine.

Fig. 3 is a sectional view of the stem of such a bulb. Fig. 4 is a sectional view of the press of a stem of such a bulb, taken on the line 4-4 of Fig. 3. Fig. 5 showsa modification of my invention in which the press is made in the bulb without the use of a separate stem tube.

50 Fig. 6 is a View of the component parts of such a bulb mounted on a'wire die block of a stem making machine.

In 1894, Burnette' and Doane disclosed in Unitedy States Letters Patent No. 516,800 a 55 method of bulb construction in which an exhaust tube such as I3'in Fig. 1 was sealed to the stem I2 of a vbulb II in a manner which permitted the protection of the exhaust tube tip aftersealf; ing-from the pump by means of a base asis-coma vlio moninelectric lamp bulbs in use today.A Their method of attaching the exhaust tube I3 to the stem tube I2, involved placing in the stem tube I2, the exhaust tube I3 containing a refractory material. The stem tube I2 was then sealed and 'pressed on to the exhaust tube I3 forming the 5 `For years since the patent to Burnette and Doane attempts have been made to apply this technique on` a production basis. To my 15 "knowledge these attempts have been largely unsuccessful due primarily to the diniculty in removing the refractory material from the opening after the press has been made. Also when it has been possible to accomplish this result, the 20 stem has been fragile at the joint 20 between the exhaust tube I3 and the press I4.

Various other methods have been suggested for maintaining the opening I6 in press I4. In making a thorough study of this matter I have found 25 that each suggested method has been subject to severe defects if it is desired to produce bulbs lon a production basis. In making my tests, I have devised a stem testing machine with which it is possible to accurately test the resistance 30 against breakage of the exhaust tube from the stem tube at the joint 20.

In practicing my invention I rigidly place a plug 24 of wire or'rod in Wire die block 21 as in Fig. 2. The wire die block, 21, is similar to that 35 used in ordinary stem making machines and is well known to those skilled in this art. I have found that it is very desirable to slightly taper the portion 26 of plug 24 which extends from wire die block 21. stem tube I2 and exhaust tube is 40 are supported by suitable means above wire die block 2l as is common' practice. Wires I1 and II'I are inserted in'the wire die block. Extensions of wires I'I and II-I are welded inserts I9 and H9 of suitable properties to properly seal 45 to the glass'when the press is formed. The leadA wires 2| and I2I welded to inserts I9 and IIS provide connection to external apparatus when the bulb is completed.

In the process of manufacturing the stem, the sequence of operations is as follows. The tapered portion 26 of plug 24 is first coated with a film 28 of nely divided material such as lamp black, gas carbon, graphite, talc or stable salts in powdered form. For this purpose I find that I can deposit a lm of carbon by smoking the plug withva gas-llame. An alternative andsomewhat preferable method from the standpoint ofV speed, reliability and simplicity of equipment required-is to coat the plug with a candida: solu- 6 tion of nely divided material such as graphite. The coating may be accomplished with a brush, spray gun, or other suitable means. One method which I have found to be particularly suitable is to use a tube slightly larger in inside diameter than plug 24 which is first dipped into the colloidal solution and then lowered over the tapered portion 26 of plug 24. A sufficient quantity of the colloidal solution is picked up by the tube to deposit evenly a coating of the desired thickness. This thickness may be readily controlled by altering the concentration of the colloidal solution.

Having prepared the film which can be done in production in a very short length of time, the wires II and II1, tubes 23 and I3 are placed in position. The machine used is essentially that which is well known in the art of stem making. In the successive operations of the machine the glass is heated and pinched to form the press I4. In one of the final operations I prefer to apply air pressure to the exhaust tube I3 causing it to expand slightly at 22. This expansion of the tube greatly strengthens it at this point because it rounds out any sharp junctions in the glass which might otherwise remain at the joint 2D where the exhaust tube I3 joins the press I4.

After passing through the annealing res the completed stern is lifted from the wire block 21. Due to the lm 28 which I have previously applied to the plug 24 on tapered portion 26, the stem may be lifted without any sticking of the glass to the plug. Without this film I have found it practically impossible to remove the glass stem.

Upon removing the stem it is found that a portion of the vfilm material has adhered to the glass on the inner Wall of opening I6. I consider this to be no disadvantage inasmuch as it causes no undesirable effect in the use of the nished bulb. If I use carbon for' the lm material, I find that that which adheres to the inner wall of opening I6 combines with oxygen in the subsequent annealing of the stem as is generally necessary in manufacturing any type of stem and consequently the carbon disappears.

For the plug 24, I have investigated the properties of various materials. I find that it is desirable touse a material of greater coefficient of thermal expansion than glass. A material such as iron which was suggested by Burnette and Doane meets this requirement. However, for continuous use I find that a material which does not corrode so readily is desirable. For this reason I prefer to use brass or silver for the plug.

In manufacturing small tubes such as shown in Fig. 5, I make the press I4 directly on the end of the bulb III. To obtain a shoulder against which to attach base 3|, I roll a ring of glass 29 in bulb III. The method for accomplishing this is similar to that used in manufacturing homeopathic vials and the like in which the glass is heated and a ring, bead or flange is rolled with a suitable tool. This process is well known and I do not claim any novelty in the method of making ring 29. The use of this method of mounting a base to a bulb having an external press, i. e a

bulb in which the wires I9 and II9 are sealed with an exhaust tube I3 directly to the bulb I believe to come within the scope of my invention.

In making the external press in this type of bulb the procedure is similar to that described above. In Fig. 6 the plug 24 is positioned in wire die block 21 which is a part of a standard type stem making machine. Tapered portion 26 of plug 24 is next coated with film 28 as described. An annular opening around the upper portion of the part of plug 24 which is within the wire die block 21 permits the insertion of exhaust tube I3. Wires 2I and I2I are placed in holes in wire die block 21 which are of proper depth to bring welded inserts I9 and II9 just above the wire die block. The extended portions I1 and II1 of the wires carrying filament I8 or other electrode assembly which may be of any desired construction, are assembled before bulb III is placed in position above wire die block 21 in the stern machine.

In the operation 0f the stem making machine the glass below ring 29 is heated and pressed on to Wires I9 and II9 and makes the seal with exhaust tube I3. After the glass is partially cooled, bulb III is removed from the machine without any sticking of the glass because of the action of lm 28 on tapered portion 26 of plug 24.

It is understood that the nature and embodiment of the invention herein described and illustrated is merely a convenient and useful form of the invention and that many changes and modifications may be made herein without departing from the spirit and scope of the invention.

What I claim as new and desire to secure by United States Letters Patent iszl. The method ,of making stems for electric lamps, vacuum tubes or similar devices requiring evacuation, which comprises coating a refractory plug with a film of finely divided material, positioning a tube over said coated plug, positioning one or more wires parallel to said plug, positioning a hollow glass body over said tube, plug, and wires, applying heat and mechanical force to cause the fusion of a solid glass mass around the refractory plug, slightly expanding the internal and external diameters of said tube and then y removing the assembly of said tube, wires and hollow glass body from said plug.

2. The method of making a bulb of the character described having an opening through the press for evacuation, which comprises placing on exhaust tube over a refractory plug, positioning a stem tube about said exhaust tube fusing said tubes and uniting them under mechanical force to form the press about the plug, removing said mechanical force, applying fluid pressure to the interior of said exhaust tube and withdrawing said plug.

3. The method of making a bulb of the character described having an opening through the press for evacuation, which comprises forming the press withan exhaust tube attached about a plug of the like to mold an aperture through the press into the exhaust tube, then producing a fluid pressure within said exhaust tube and subsequently removing said press from said plug.

4. The method of making stems for electric lamps, Vacuum tubes or similar devices requiring evacuation, which comprises coating a refractory plug with a film of nely divided material, positioning a tube over said coated plug, positioning one or more Wires adjacent to said plug, positioning a hollow glass body over said tube, plug and wires, heating the glass and wire to a temperaturt suiiiciently high to fuse the wire to the glass, molding the glass about the wires and the plug, slightly expanding the internal and external dlameter of said tube and then removing the assembly of said tube, Wires and hollow glass body from said plug.

ARCHJE J. MCMASTER. 

